When using mould cores known hitherto, the task of setting and stripping the mould is both complicated and time consuming. The cost of the moulds and associated mould cores is also high. Contributory hereto is, inter alia, the handling difficulties experienced as a result of the completely closed core space.
In an attempt to avoid these difficulties, one method proposes that the mould core is made of steel and supplemented with loose mould parts. In this way, it is possible to strip the steel core separately towards one free side, and to then loosen the remaining mould parts, which form the recesses in the cast concrete element, by forcing said parts inwardly into the free core space created when removing the steel core.
Even this method, however, requires doubling of the mould setting operations and time consuming, heavy work in difficulty reached spaces within the mould core. In addition, the loose mould parts must be cleaned and handled, which also means heavy and difficult work.
In U.S. Pat. No. 2,680,276 (Filangeri) there is described a cesspool mold of large dimensions including inner and outer sectional walls to provide a moulding space, i.e. there is no mould core like in the present invention. The inner wall sections are provided with tubular guides for core pins which are projectable across the moulding space to form drainage openings in the cesspool wall. When assembling the mould a workman enters through a manhole and connects a plate holding the core pins with a central post, so that it will be possible to displace the core pins from outside of the mould. The arrangement is complicated and expensive and possible to use only in very big moulds.